Photographic diffusion transfer process for producing multiple direct positive copies



United States Patent PHOTOGRAPHIC DIFFUSION TRANSFER PROCESS FOR PRODUCING MULTELE DIRECT POSITIVE COPIES Edward I. Stanley, Lake Mohawk, John J. Dughi, Lake Owassa, and Walton Arthur Hey, Sussex, N. .l'., as signors to Sperry Rand Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application July 19, 1955 Serial No. 523,098

8 Claims. (Cl. 96-29) This invention relates to photographic diffusion transfer processes for the production of direct positive image copies. More particularly, this invention relates to photographic difiusion transfer processes for obtaining multiple direct positive copies from an exposed silver halide emulsion coating, and to new processing solutions for performing such multiple copy transfer processes.

Photographic diffusion transfer processes for obtaining direct positive image copies from exposed silver halide emulsion layer coatings are well known, and are described, for example, in United States Patent 2,352,014, German Patent 764,572 and Swiss Patent 240,472. Direct positive diffusion transfer processes described in the aforementioned patents are characterized by the imagewise diffusion transfer of silver halides, dissolved in silver halide solvents, from an exposed and developed silver halide emulsion layer into a light insensitive reception layer coating containing development nuclei and in which reception layer the diffusion transferred silver halides are reduced to metallic silver. In one widely adopted modification of such direct positive transfer processes, the light sensitive emulsion layer and the light insensitive reception layer are each coated on separate supports. After exposure, the silver halide emulsion layer is brought into close contact with the reception layer while the exposed emulsion layer is being rapidly developed in the presence of a silver halide solvent. After the development transfer process has progressed for half a minute, more or less, the contacted layers are separated to obtain a positive image copy on the reception layer coated support.

In direct positive diffusion transfer processes characterized as described above, the image-wise exposed silver halide emulsion layer, while being held in close contact with a light insensitive reception layer containing finely dispersed development nuclei, is developed in the presence of a silver halide solvent. During development exposed silver halides are reduced to metallic silver comprising a negative image copy of the original image and unexposed silver halides are dissolved by the silver halide solvent and are transferred to the reception layer by diffusion migration of the dissolved silver salts. In the reception layer containing development nuclei, the image wise transferred silver salts are reduced by the developer, with the development nuclei catalyzing the reduction, to metallic silver comprising a positive image copy of the original image.

Development nuclei for catalytically accelerating reduction of the transferred silver salts in the reception layer, include substances which, above an optimum concentration, are prone to cause fog in silver halide emulsions, and below which concentration, increase emulsion sensitivity, i. e., the developability of silver halide emulsions. Accordingly, such substances have been referred to as photographic fogging agents. Colloidal silver, colloidal silver sulfide and colloidal gold are advantageously useful as development nuclei in reception lay- Patented May 13, 1958 ers. Moreover, other substances are useful which do not act as development nuclei in themselves but which react with the diffusing silver salts to form development nuclei such as, for example, sodium sulfide and sodium thiosulfate;

The above described photographic transfer processes are especially useful for therapid copying of documents, drawings, letters and other indicated records, including written and imprinted records, in business, industry and government. Extensive use and commercial success of such processes are due, in part, to the fact that such processes have been adapted for use in business office rooms, under ordinary ofiice illumination conditions, and without requiring skill'in photographic techniques; Performance of such processes is also considerably simplified by the use of compact, motor driven processing machines. Such machines wet at least the exposed photographic emulsion coated paper with processing solution, squeegee the Wetted paper face-to-face with the coated surface of a reception paper at uniform lineal speeds between pressure rollers which, at the same time, expel excess processing solution absorbed by the paper itself and the water absorptive, light sensitive coating thereon. The design, construction and mode of operation of suitable processing machines are described, for example, in U. S. Patents 2,657,618 and 2,664,801.

A number of other types of photographic processes involving exposure of photosensitive silver-halide emulsion coatings to an original record, followed by chemical processing of the so-exposed coating, are known for preparing positive copies of records such as documents, letters, drawings and the like. Generally speaking, these other. well known photographic duplicating processes are characterized by requiring the preparation of an intermediate or negative, photographic record of the original, from which intermediate record one or more positive or duplicate copies of the original are obtained by well known duplicating techniques. Such techniques include light exposure printing through the intermediate record onto a light sensitized copy material and the processing of the printed copy material to obtain a positive copy. In common with many known photographic duplicating processes, photographic diffusion transfer processes also requirean intermediate negative record in a silver halide emulsion layer coating for each positive copy. For many purposes, however, it is necessary to obtain several copies of a letter, order, communication and the like, and to obtain the several copies with a maximum of speed and a minimum of cost of materials. Photographic diffusion transfer processes which require an intermediate negative record for each positive copy are at a disadvantage compared with several other well known photographic duplicating processes,.for preparing two, or several, copies where both economy in cost of materials and speed of producing the copies are required. Moreover, no suggestions have appeared for solving the problem of producing up to four or five positive copies of satisfactory quality from the same diffusion transfer process intermediate negative. German Patent 764,572 includes mention of the possibility of obtaining several positive copies from the same intermediate negative by diffusion transfer processes. Swiss Patent 240,472 sug:

gests using silver halide emulsion coatings which are relatively low in silver halide content for the intermediate negative record material for producing two or three positive copies from the same intermediate negative record.

having poor gradations and weak images ranging from brownish red to reddish yellow in color.

Several inherent features unique to the above described diffusion transfer processes for producing direct positives also appear to contribute to the problem of obtaining multiple positive copies of satisfactory gradation and image tone. Features inherent in and characteristic of such processes include, (1) the two different types of development nuclei present during processing, i. e., (0)

nuclei produced by exposure of the silver halide emulsion grains and (b) nuclei prepared by chemical reaction in the reception layer or prepared as a coating composition and subsequently coated in a layer on the reception material support; (2) reduction of exposed silver halides, dissolution of undeveloped silver halides in a silver halide solvent, and reduction of said dissolved silver salts, all proceeding in the presence of the two different types of development nuclei, each type being in separate, adjacent layers; and (3) reduction by the developer of exposed silver halides in the photographic emulsion layer and concomitant reduction of silver salts dissolved by the silver halide solvent, producing negative and positive silver images in separate layers of hydrophillic colloid binding agents.

Another inherent feature of the above described processes is a limitation common to reversal processes in general and including the present modification, namely, one and the same photo-sensitive silver halide emulsion layer coating provides the silver salts which yield the metallic silver for producing not only the negative image intermediate but also the positive image. Thus, in a silver halide emulsion coating for use in reversal processing, the amount of silver halides available for forming a positive image varies inversely with the amount of silver halides reduced during the initial or first development. Accordingly, the amount of image-wise or initial exposure is of prime importance in determining the amount of silver halides available for producing positive images in reversal processes. Additionally, the amount of silver halides made developable and subsequently reduced to metallic silver due to the fogging action of the developer, room illumination, and other fogging actions, further reduces the total of silver halides available for forming the positive image.

In producing copies by the diffusion transfer type of reversal processes in business offices etc., even with somewhat subdued room illumination, varying degrees of overall fogging of the light sensitive photographic emulsion coatings may occur before the image-Wise exposure thereof, after the image-wise exposure but before processing, after processing, or at several of these stages. Where only a single copy is obtained from an exposed emulsion layer, fogging by room illumination, aerial oxidation of the developer, chemiluminescence etc., after processing are of no consequence. However, post-processing fogging of the silver halide emulsion coating assumes prime importance in the additive effect of fogging actions contributing to the causes for failure to obtain multiple positive copies from the same silver halide layer by prior diffusion transfer reversal processes.

An object of the present invention is to provide an improved photographic diffusion transfer process for obtaining multiple duplicate copies of original images. Another object is to provide a photographic diifusion transfer process for producing multiple direct positive copies from the same exposed silver halide emulsion coating. A further object is to provide a photographic diffusion transfer process employing the same exposed silver halide emulsion layer coating for producing multiple direct positive copies having image deposits which are non-selective in color absorption. A still further object is to provide developing compositions for producing multiple direct positive copies from the same exposed silver halide emulsion layer coating by photographic diffusion transfer processes. Still further objects will be apparent from the following description of the invention.

According to the present invention multiple direct positive copies of an original record are obtained by forming a latent image of the record in a silver halide emulsion layer and contacting said emulsion layer with a reception layer containing development nuclei, said contacting being in the presence of a silver halide developer containing a silver halide solvent, a fixation acelerator, a latent image desensitizer and a gelatin softciting agent, separating the layers and recontacting said silver halide emulsion layer with another reception layer in the presence of said developer.

More particularly, it has been found that upon contacting an exposed silver halide emulsion layer and a reception layer containing development nuclei in the presence of an alkaline developer containing a silver halide solvent, if there are also present an accelerating agent increasing the solvent action of the silver halide solvent, and a non-staining latent image desensitizer, and a gelatin softening agent, after separating the contacted layers to obtain the positive copy produced in the reception layer, the silver halide emulsion layer may be recontacted with a new reception layer in the presence of said developer and re-separated to obtain a second positive copy having image tone and gradation comparable to the first copy. Moreover, the same silver halide emulsion layer may be re-contacted with still another new reception layer in the presence of the improved developer and separated to obtain a third copy having good gradations and image color characteristics. The re-contacting and separating operations may be repeated still further, each time with the same silver halide coating but with a new reception layer, to obtain four, five or more copies of satisfactory quality as to color of image and gradation.

Silver halide emulsions useful in performing the multiple copy diffusion transfer process of the present invention include silver chlorobromide emulsions, silver bromide emulsion containing silver chloride, and silver chloride emulsions, all of which emulsions may also contain small amounts of silver iodide. When speed of transfer is desirable, silver halide emulsions containing a substantial proportion of silver chloride are preferable. However, where minimum exposure time is desired, rapid silver bromide emulsions containing some silver chloride are advantageous.

Developing compositions for difiusion transfer processes include organic developing agents such as, for

example, hydroquinone, N-methyl-p-amin-ophenol sulfate and l-phenyl-S-pyrazolidone, caustic alkalis such as sodium and potassium hydroxides, preservatives such as sodium sulfite and potassium metabisulfite, development restrainers such as potassium bromide and sodium bromide, and water soluble thiosulfates such as sodium thiosulfate. The improved developer compositions for obtaining multiple positive copies by such diffusion transfer processes contain, in addition to the above, gelatin softening agents, latent image desensitizers and fixation accelerators.

The compositions for coating the photosensitive silver halide emulsion layers, light insensitive reception layers, and layers of top-coatings over some types of light sensitive layers useful in transfer processes contain natural or synthetic hydrophilic, film-forming colloids, or mixtures thereof, as the binding agent component. Suitable colloids include gelatin, gum arabic, sodium alginate, cellulose derivatives including methyl cellulose, sodium carboxymethyl cellulose and hydroxyethyl cellulose, and hydrolyzed vinyl polymers including polyvinyl alcohol, partially hydrolyzed polyvinyl acetates, polyvinyl pyrrolidone and completely hydrolyzed ethylene/vinyl acetate interpolymers of low ethylene content. The aforementioned coating compositions also contain one or more hardening or tanning agents which insolubilize coated layers of hydrophilic colloid binding agents and minimize the swelling thereof in caustic alkali processing solutions such as are used in diffusion transfer processes. Moreover, hardening of the coated hydrophilic colloid layers renders the same resistant to physical deformation and damage due to reticulation, abrasions, pitting, and other disruptions in the planar continuity of the coated layers. Prevention of such deformation and damage to coated layers is even more important in the present multiple copy transfer reversal processes than in photographic duplicating processes which do not employ image-wise diffusion of silver salts between contacted layers of hydrophilic colloid binding agents. Suitable hardening agents include formaldehyde and formaldehyde forming compositions such as hexamethylenetetramine and paraformaldehyde, dialdehydes such as glyoxal and paraglyoxal, and inorganic salts of chromium, zirconium and aluminum. However, substances which harden or otherwise render gelatin and other binding agent colloids insoluble and resistant to physical damage, also diminish the permeability of the insolubilized colloid layers, and consequently, hinder diffusion transfer of dis solved silver salts from the light sensitive layer to the reception layer. It was discovered that the permeability of hardened or otherwise insolubilized layers of colloid binding agents was increased, with resultant acceleration 2 in diffusion transfer of dissolved silver salts, by having present during processing one or more gelatin softening agents.

Gelatin softening agents are characterized by their ability to reduce the setting point of gelatin solutions and have also been referred to as gelatin liquefying agents. Such liquefying agents include a wide variety of substances as, for example, urea, potassium nitrate, potassium iodide, potassium thiocyanate, sodium nitrate, sodium salicylate, barium chloride, calcium chloride, magnesium chloride, chloral hydrate and alpha-naphthalene sulfonic acid sodium salt.

A large number of organic dyestuffs and metal salts are known which decrease or destroy latent images in silver halide emulsions thus delaying or inhibiting the development thereof. Among a wide diversity of latent image desensitizers, the non-staining metal salt class of desensitizers, particularly the chlorides and bromides of copper, zinc, mercury, manganese, barium, strontium and .cadmium have been found advantageous latent image desensitizers in the present transfer processes. Cupric chloride,

cupric bromide, mercuric chloride, zinc chloride and manganese chloride have shown exceptional utility in the present processes for inhibiting the additive effect of overall fogging actions.

Fixation accelerators include potassium chloride, sodium chloride and ammonium chloride. Among fixation accelerating agent compounds, sodium chloride has been discovered to be significantly outstanding in its effect of producing deep black tone images on multiple direct positive copies when used in the presence of a latent image desensitizer and a gelatin softening agent in the present transfer processes. The action of fixation accelerators in improving the tone quality of the positive images obtained by the present processes is not fully understood but is believed to be due in part to, or associated with, the formation of complex silver halide ions which have greater solubility in the silver halide solvent, thus increasing the concentration of reducible silver salts available to the catalyzing action of the development nuclei.

The following examples serve to illustrate this invention without limiting, however, the scope thereof.

Example 1 Grams Sodium sulfite, anhydrous 55.0 N-methyl-p-aminophenol sulfate 2.2 Hydroquinone 6.3 Sodium hydroxide 9.5 Sodium thiosulfate, crystals 6.3 Potassium bromide 2.0

Sodium chloride 5.0 Cupric chloride 0.02 Potassium nitrate 1.0

Water to 1 liter.

After moistening, the exposed emulsion coating was immediately squeegeed into contact with the coated layer of the reception paper, and maintained in contact for 5 to seconds, after which the papers were stripped apart revealing a neutral black image positive copy of the original. Immediately after separating the two papers, the photographic emulsion coated paper was remoistened with processing solution and again squeegeed into contact with the coated layer of another reception paper, held in contact for 5 to 15 seconds, and then the papers were separated to obtain a neutral black image second copy. The steps of remoistening the emulsion coating of .the photographic paper, recontacting the same with a new reception layer, maintaining the contact for 15 to seconds, and separating the contacted layers, were repeated to obtain a third, and a fourth positive'copy, of satisfactory image quality, from the same exposed photographic emulsion layer.

Example 2 Double weight photographic paper stock coated with a high contrast chlorobromide photographic emulsion was reflex exposed with a printed page of advertising copy containing both descriptive wordage and a half-tone reproduction of a continuous-tone photographic print. A reception layer material was prepared by coating single weight photographic paper stock with an aqueous solution comprised as follows:

Sodium carboxymethyl cellulose 0.6 p e r c e nt b y weight. Gelatin 2.1 percent by weight. Formaldehyde (37-40%) 30 mL/kilogram of binding agents.

gm./kilogram of binding agents. Colloidal silver sulfide 0.8 gm./kilogram of I binding agents. and drying. the coated reception layer. The exposed photographic emulsion layer coating was impregnated with processing solution of the following composition:

S oiiium thiosulfate, anhydrous- Water to 1 liter.

and immediately pressed into contact with the coated layer of a sheet of reception material. After 15 seconds total transfer contact between the exposed photographic layer and the reception layer, the respective paper supports were pooled apart yielding the photographic emulsion coated paper carrying a developed negative image of the original and the reception paper carrying a positive image of neutral black color in the'dark, middle-tone, and highlight density areas of the positive copy of the halftone reproduction. Three additional positive copies,

comparable to the first copy in quality of image color and gradation, were obtained from the same exposed emulsion coating layer by repeating the processing steps, each time with a new sheet of reception material, and maintaining close contact between the layers for total transfer periods of 18, 25 and 40 seconds, for the 2nd, 3rd, and 4th copy respectively.

Example 3 A document copying paper comprising a high contrast chlorobromide photographic emulsion coated on double Weight paper stock was exposed as described in Example 2 and contacted with reception material, prepared as also described in the same example, in a processing solution of the following composition:

Grams Sodium sulfite, anhydrous 5O l-phenyl-3-pyrazolidone 1.3 Hydroquinone 13 Sodium hydroxide 7.3 Sodium thiosulfate, crystals 13 Potassium metabisulfate 3.2

Benzotriazole 0.3 Potassium bromide 3.2 Sodium chloride 15 Cupric chloride 0.06

Ptoassium nitrate 9 Water to 1 liter.

Following the procedure steps described in the previous example, six positive copies of satisfactory gradation and neutral tone of images were obtained by maintaining diffusion transfer contact between the exposed silver halide layer and reception layer coatings as follows:

Total contact time, seconds lst copy 15 2nd copy 17 3rd copy 20 4th copy 5th copy 6th copy to 70 Example 4 Using photosensitive silver halide and reception layer coatings as described in Example 2 and following the procedures therein described, four positive copies having dense neutral black images of good gradation quality were obtained using a processing solution of the following composition:

Water to 1 liter.

and maintaining diffusion transfer contact between the exposed silver halide layer and reception layer coatings for a total of 15 to 25 seconds for the first and second copies and for 30 to 40 seconds for the third and fourth copies.

Example 5 Five positive copies having neutral black images and gradation quality comparing favorably with the original printed copy were obtained by using light sensitive and reception layer coated papers as described in Example 2 and a processing solution similar to the one described in the previous example except that 6 grams of manganese chloride, MnC1 .4H O, were substituted for the mercuric chloride in the processing solution of Example 4 and the solution was filtered before use to remove the precipitate. Diffusion transfer contact between the exposed silver halide emulsion and reception layer coatings was maintained for 45 to 60 seconds for the fifth positive copy, depending on the contact times for the first four copies.

Example 6 An equal weight of cadmium chloride, CdCl .2 /2H O, was substituted 'for the mercuric chloride in the processing solution composition of Example 4. After filtering to remove the precipitate, the solution was used in the procedure described in the previous example to obtain five positive copies having dense black images of good gradation quality from the same exposed photographic emulsion "layer coating.

Example 7 Five positive copies of satisfactory image quality were obtained by following the procedure described in Example 5 using the processing solution composition of Example 4 except, however, that the sodium chloride was increased to 40 grams and 3.5 grams of strontium bromide, SrBr .6I-I 0, were substituted for the potassium bromide of the above described solution.

Example 8 A processing solution similar in composition to that of Example 4 was prepared, substituting however, 2.5 grams of cadmium bromide, CdBr .4H 0, for the potassium bromide of the earlier example and increasing the concentration of sodium chloride to 40 grams per liter of solution. The precipitate was removed by filtration and the filtered processing solution was employed in the procedure described in the same example to obtain four positive copies having dense black images.

Example 9 Four positive copies of satisfactory image quality were provided by the same exposed high contrast chloro'bromide emulsion layer coating 'by following the procedure of Example 8 and using a similar processing solution with the exception that 3.5 grams of ammonium bromide, NH Br, were substituted for the cadmium bromide used in the process of the previous example.

Example 10 The multiple copy diffusion transfer procedure of Example 4 was repeated with a processing solution similar to the composition given in the example with the exception that 12 grams of barium chloride, BaCl .2H O, were substituted for the mercuric chloride described in the previous example and the solution was filtered to remove the precipitate. Using the filtered processing solution, four black image positive copies of satisfactory gradation were obtained from the same exposed photosensitive silver halide emulsion layer coating.

Example 11 Four positive copie's having sharp, dense black images of excellent gradation quality were obtained by following the procedure described in Example 4 but using a processing solution of the following composition:

9 Example 12 In general, little or no control of temperature of diffusion transfer reversal processing solutions is provided in actual use in business ofiices and the like. Under such conditions, the exposed silver halide emulsion layer may fail to develop due to low temperature of the processing solution. Contra-wise, processing solutions too high in temperature may cause the contacted layers of hydrophilic, film-forming colloids to adhesively laminate with each other thus preventing their subsequent separation without physical damage to one or both layers. Prevention of such physical damage is important where only one positive copy is desired, and becomes imperative if several copies are to be obtained from the same negative image layer. The propensity for contacted layers of hydrophilic colloids to adhesively laminate with each other in multiple copy transfer processes is considerably inhibited when the contacted layers comprise difierent hydrophilic, film-forming colloids or mixtures of such colloids. The coated layer of the reception material of Example 2 illustrates one class of mixed colloid coatings.

Another reception material for the present multiple 2 copy difiusion transfer process was prepared 'by coating medium weight photographic paper stock with a composi tion comprised as follows:

Gelatin 3.8 percent by weight.

Polyvinylpyrrolidone 2.2 percent by weight.

Sodium thiosulfate, anhydrous 60 grn./kilogram of binding agents.

Colloidal silver sulfide 0.37 gm./kilogram of binding agents.

Formaldehyde (37-40%) 36 ml./kilogram of binding agents.

Reception materials prepared as described produced positive copies having rich black images by the above described multiple copy procedures and exhibited remarkably little tendency, or no tendency at all, to laminate with the silver halide emulsion layers during transfer contact with same.

Example 13 Other reception materials useful in the present processes were prepared 'by coating a paper support with an aqueous solution comprising:

Example 14 The photosensitive silver halide emulsion layers may also be provided with an anti-abrasion top-coating of hydrophilic film-forming colloids, or mixtures of such colloids, as another means for preventing the light sensitive emulsion and reception layers from forming cemented laminates with each other while being held in diffusion transfer contact. Light sensitive silver halide emulsion coatings similar to those of Examples 1 and 2 were top-coated with anti-abrasion layers comprising a mixture of sodium carbomethylcellulose. The antiabrasion layers may also contain a developing agent, for which use hydroquinone is a preferred example, and a l0 slightly acidic preservative such as, for example, potassium metabisulfite.

In a modification of the above described procedures, the photosensitive silver halide emulsion is exposed by transmission printing, that is to say, by light transmitted through the original record instead of by light reflected by the record. With such directly exposed silver halide emulsion coatings and the present multiple copy transfer processes it is possible to obtain eight to ten positive copies from the same exposed silver halide emulsion coating.

Since the total amount of silver halides in any given emulsion coating which are available for forming positive images varies inversely with the silver halides developed as the negative image, the amount of image-wise exposure is a controlling factor in the number of copies obtainable from the coating, the number of copies increasing with under-exposure and decreasing with over-exposure. Moreover, the length of time the silver halide emulsion and reception layers remain in contact with each other is also a factor in determining the number of copies obtainable from a given exposure of the silver halide emulsion layer.

From the foregoing description it is apparent that the process herein described provides a means for obtaining a negative silver image copy of an original record and also a number of individual positive silver image copies of the same record, each image copy being formed in its respective layer of hydrophilic film-forming colloid layercarried by a separate support, by reduction of silver salts supplied by one and the same photosensitive silver halide emulsion layer. Thus the process of this inventioii provides a simplified means for the rapid and economical duplication of records, drawings, documents and the like.

The invention having been described and as many Widely different embodiments thereof can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not to be limited except as defined by the claims.

What we claim is: I

l. A process for obtaining multiple copies from an exposed silver halide emulsion layer which comprises contacting said emulsion layer with a reception layer containing development nuclei, said contacting being in the presence of an alkaline silver halide developer containing a silver halide solvent and a fixation accelerator selected from the class consisting of alkali metal and ammonium chlorides, and a latent image desensitizer selected from the class consisting of cupric, mercuric, zinc, arid manganese chlorides, and a gelatin softening agent selected from the class consisting of alkali metal and ammonium nitrates, separating the layers and recontacting the silver halide emulsion layer with another reception layer in the presence of said alkaline developer.

2. A process for obtaining multiple positive copies from an exposed silver halide emulsion layer which comprises contacting said emulsion layer with a reception layer containing development nuclei, said contacting being in the presence of an alkaline silver halide developer containing a silver halide solvent and a fixation accelerator selected from the class consisting of alkali metal and ammonium chlorides, and a latent image desensitizer selected from the class consisting of cupric, mercuric, zinc, and maga- I nese chlorides, and a gelatin softening agent selected from the class consisting of alkali metal and ammonium nitrates, developing a negative image in the silver halide emulsion layer and a positive image in the reception layer, separating the layers, recontacting the silver halide emulsion layer with another reception layer in the presence of said alkaline developer and developing another positive image in said otherreception layer.

3. The method of photographic duplication which comprises exposing a silver halide emulsion layer to a record and contacting said emulsion layer with a reception layer containing development nuclei, said contacting being in the presence ofan alkaline silver halide developer containing a silver halide solvent and a fixation accelerator selected from the class consisting of alkali metal and ammonium chlorides, and a latent image desensitizer selected from the class consisting of cupric, mercuric, zinc, and manganese chlorides, and a gelatin softening agent selected from the class consisting of alkali metal and ammonium nitrates, developing a negative image of said record in the silver halide emulsion layer and a positive image of said record in said reception layer, separating the layers and recontacting said silver halide emulsion layer with another reception layer in the presence of said alkaline developer and developing another positive image in said other reception layer.

4. The method of photographic duplication which comprises exposing a silver halide emulsion layer to a record and contacting said emulsion layer with a reception layer containing development nuclei, said contacting being in the presence of an alkaline silver halide developer containing a thiosnlfate silver halide solvent and a fixation accelerator selected from the class consisting of alkali metal and ammonium chlorides, and a latent image desensitizer selected from the class consisting of cupric, mercuric, Zinc, and manganese chlorides, and a gelatin softening agent selected from the class consisting of alkali metal and ammonium nitrates, developing a negative image of said record in the silver halide emulsion layer and a positive image of said record in said reception layer, separating the layers and recontacting said silver halide emulsion layer with another reception layer containing development nuclei in the presence of said alkaline developer and developing another positive image in said other reception layer.

5. The process of claim 1 wherein the silver halide solvent is sodium thiosulfate.

6. The process of claim 1 wherein the fixation accelerator is sodium chloride.

7. The process of claim 1 wherein the latent image desensitizer is cupric chloride.

8. The process of claim 1 wherein the gelatin softening agent is potassium nitrate.

References Cited in the file of this patent UNITED STATES PATENTS 2,663,641 Rott Dec. 22, 1953 2,675,313 Yutzy et a1 Apr. 13, 1954 2,712,995 Weyde July 12, 1955 2,725,298 Yutzy et al Nov. 29, 1955 2,740,717 Yutzy et al. Apr. 3, 1956 

1. A PROCESS FOR OBTAINING MULTIPLE COPIES FROM AN EXPOSED SILVER HALIDE EMULSON LAYER WHICH COMPRISES CONTACTING SAID EMULSION LAYER WITH A RECEPTION LAYER CONTAINING DEVELOPMENT NUCLEI, SAID CONTACTING BEING IN THE PRESENCE OF AN ALKALINE SILVER HALIDE DEVELOPER CONTAINING A SILVER HALIDE SOLVENT AND A FIXATON ACCELERATOR SELECTED FROM THE CLASS CONSISTING OF ALKALI METAL AND AMMONIUM CHLORIDES, AND A LATENT IMAGE DESENSITIZER SELECTED FROM THE CLASS CONSISTING OF CUPRIC, MERCURIC, ZINC, AND MANGANESE CHLORIDES, AND A GELATIN SOFTENING AGENT SELECTED FROM THE CLASS CONSISTING OF ALKALI METALAND AMMONIUM NITRATES, SEPARATING THE LAYERS AND RECONTACTING THE SILVER HALIDE EMULSION LAYER WITH ANOTHER RECEPTION LAYER IN THE PRESENCE OF SAID ALKALINE DEVELOPER. 